1. Field of the Invention
This invention relates to a method for improving the adhesion of automobile body putty to galvanized steel in the repair of automobile body parts.
2. Description of the Prior Art
Automobile and truck bodies have generally been made from mild steel sheet metal. Steel comprises any alloy that contains the element iron as the major component and small amounts of carbon as the major alloying element. These alloys are more properly referred to as carbon steels, and make up well over 90% of the tonnage of steels produced throughout the world.
Low-carbon steels, also referred to as mild steels, usually contain less than 0.25% carbon. These steels are easily hot-worked and are produced in large tonnages for beams and other structural applications. The medium-carbon steels contain between 0.25 and 0.70% carbon, and are most frequently used for machine components that require high strength and good fatigue resistance. High-carbon steels contain more than 0.7% carbon and are in a special category because of their high hardness and low toughness.
It has been well known to repair the dented or gouged steel surfaces of automobile body parts by applying a putty composed of a thermoset resin, such as an unsaturated polyester resin or an epoxy vinyl ester, fillers, promoters, catalysts and other additives, to the damaged metal surfaces. The putty is allowed to harden and is subsequently shaped to conform to the desired contour of the automobile body part.
Standard body putty has successfully been used to repair damaged steel surfaces of automobile bodies. However, rust and corrosion have increasingly become major problems for automobiles whose bodies are manufactured from mild steel.
In order to minimize corrosion, the automobile industry is now considering the replacement of mild steel with zinc-coated or galvanized steel. It has been found that standard body putties that are suitably used with mild steel sheet have poor adhesion to galvanized steel. Thus, an urgent need exists for a means of improving the adhesion of automobile body putty to galvanized steel.
U.S. Pat. No. 4,525,427 to Bayha et al relates to polyester compositions capable of forming a thin film that adheres to metal and plastic substrates, such as steel, and are particularly useful in repairing automobile bodies. These compositions are referred to as "body putty primers." Bayha also discloses that the metallic surface may also be chemically etched to maximize adhesion of surfacing materials to the metal surface.
U.S. Pat. No. 4,531,275 to Kelly discloses a method for repairing automobile bodies made of sheet metal that have been damaged by rust or through an accident. The method involves removing the damaged area and replacing it with a metal patch secured behind the opening with fasteners. The depression behind the opening is then filled with body filler. The metal patch that is used can be galvanized steel.
U.S. Pat. No. 4,732,633 to Pokorny discloses a method for repairing the surface of a damaged metallic body of sheet metal by applying a corrosion resistant patch to the damaged surface so that the back side of the patch is in contact with and adheres to the portion of the bare metal adjoining the damaged surface.
U.S. Pat. No. 4,148,122 to Phillips relates to the repair of automobile bodies made of sheet metal which have been damaged by rust and involves providing a cavity behind the hole or rust area and filling the cavity with a moldable plastic material, then applying a polyester resin filler to the area and grinding the surface of the filler to conform to the surface of the automobile body.
U.S Pat. No. 2,150,929 to Kohler discloses a method for protecting a galvanized metal sheet that has been bent to such an extent that cracking or flaking of the galvanized coating occurs. A mercury amalgam is used to form a protective coating at the bend.
U.S. Pat. No. 4,308,118 to Dudgeon discloses mineral filled epoxy resin compositions that are curable on exposure to heat and ultra violet radiation.
U.S. Pat. No. 2,886,420 to Troy et al discloses a process and apparatus for maintaining the activity of a ferric chloride etching bath used to etch metals such as copper, tin, aluminum and zinc.
U.S. Pat. No. 3,726,707 to Prosser et al relates to the treatment of steel prior to the deposition of a porcelain enamel ground coat or cover coat.
U.S. Pat. No. 3,824,136 to Gilbert discloses a process for chemical milling of fluidic aluminum wafers The process involves spraying thin aluminum sheets with an etching solution consisting of ferric chloride, hydrochloric acid and water.
U.S. Pat. No. 4,482,426 to Maynard et al discloses a method for etching shaped apertures into a strip of nickel-iron alloy with a ferric chloride etchant.
U.S. Pat. No. 4,567,067 to Keal discloses a process for treating the surface of aluminum killed steel for subsequent porcelain coating, with particular application to porcelain coated appliances. The process employs an aqueous ferric sulfate etching solution.
U.S. Pat. No. 3,957,669 to Tulsi et al discloses a method for chemically etching steel prior to metal plating which can be followed by enameling.